It is known to provide a container by attaching to a cylindrical container body at one or both ends a respective closure member which is generally disk-shaped and has an outer edge which can be locked to the rim of the container body by folding or rolling the rim of the container body and the edge portion of the closure member together.
The closure member can be, as has been indicated, the top or cover of the container or a bottom thereof and generally the fold or rolled interlock between the closure member and the container body lies along the exterior of the container to reinforce the latter and protect the container against shocks during movement thereof.
From M. Nowicki: Laser in Elektroniktechnologie und Materialbearbeitung, Akademische Verlagsgesellschaft Geest & Portig K.-G., Leipzig 1982, it is known to weld sheet metal using a laser beam.
Various possible weld techniques for containers are also described and illustrated in German Patent document DE-OS 36 00 532 although a totally satisfactory technique for both mechanically securing closure members on a container and sealing seam is not here described.
German Patent Document DE-OS 37 06 916 discloses the connection of bottoms and covers of containers with the respective container bodies by the formation of folds or rolled-together portions in conjunction with a welding of these portions by means of a laser beam where these portions overlap to mechanically strengthen the fold and effect a sealing thereof.
In carrying out the latter process and in general with laser beam welding, it has been found that even slight deviations of the focus of the beam may be detrimental to a reliable sealing and mechanical connection of the overlapping parts. Furthermore, when bright sheet metal is to be used, the reflection of the laser beam may be such that sufficient energy is reflected that an unreliable weld can be formed. This also applies generally to the welding of aluminum sheet metal and even white sheet metal of other types.